This application relates to a novel optical fiber laser delivery system and the method of using the same. Such delivery systems are now used for certain types of surgery, such as arthroscopic surgery.
Laser radiation is used in surgical applications where the cutting of tissue is desired, or where the target tissue, such as a tumor, is to be destroyed. In such systems, various types of laser radiation have been used i.e. both continuous wavelength and pulsed, the radiation being passed through an optical fiber, and to the fiber tip. To achieve better cutting efficiency, the fiber tip is placed immediately adjacent the tissue target.
We have found that high energy pulsed laser radiation provides an effective means for such tissue destruction. For example, we have found that very effective delivery of radiation occurs where energies of two joules over a pulse of 350 microseconds are delivered at a frequency of ten hertz.
While the use of high energy pulsed radiation is effective for the destruction of tissue, we have found that catastrophic damage to the tip of the optical fiber carrying such radiation likewise occurs in many cases. Clearly, such damage is costly from a reliability standpoint. More importantly, failure of the fiber tip during surgery could lead to the deposit of debris from the destroyed tip in the patient's body.
Tip breakdown results from a number of mechanisms. For example, there may be inherent structural weaknesses arising from manufacture, such as microcracks and polishing or cleaving defects. More importantly, when sufficient laser power is delivered through a fiber to various types of tissue in a water or other medium, cutting is achieved by rapid vaporization of the water contained in the material. The resultant unbalanced pressure produces high velocity fragments which abrade and erode the materials used in the delivery device. In particular, we have found that the stainless steel and the glass components of the end piece are eroded at moderate rates, while other softer materials such as adhesives used in the manufacture of the handpiece and the fiber buffer erode much more rapidly.
Thus, it would be advantageous to provide a contact optical fiber laser delivery system for surgery wherein the delivery system was designed to minimize damage to the fiber tip arising from exposure to the forces generated when the fiber is used to transmit high energy laser radiation to the surface of the tissue in question.
It is well known with respect to fiber optics that a bare glass fiber has a very much lower tensile strength than a fiber which has been coated by a plastic. (The plastic coating is often called a buffer or "cladding.") In one particular example, we found that 480 micrometer diameter bare fibers broke when wrapped around a 5 centimeter diameter mandrill, while the same fibers when protected by a silicone buffer could be wrapped around a 2 centimeter mandrill without breakage.
In many applications of the laser in medicine, it is desirable to transmit the laser through a bent fiber in order to reach otherwise inaccessible locations. In order to reduce breakage of the fiber, it is thus desirable to have a buffer on the bent fiber. However, as noted above, the buffer material is subject to relatively fast erosion. Accordingly, it would be desirable to provide a probe which can be bent but which is not subject to rapid erosion.